Refining mineral oils



1944- H. G. M. FISCHER 27,338,579

REFINING MINERAL. OILS Filed March 22, 1941 JULFUR 26 55771104 W szrruvc20m: zo- I I j I v I (I K I 7425;); 29 g low:

35 l Jim; 37

ST RAGl Patented Jan. 4, 1944 REFINING MINERAL OILS Herbert G. M.Fischer, Westfield, N. 1., assignor to Standard Oil Development Company,a corporation of Delaware Application March 22, 1941, Serial No. 384,677

Claims.

The present invention is concerned with the refining of mineral oils.The invention is more particularly concerned with the removal ofobjectionable sulfur compounds, as for example, mercaptans frompetroleum oils, especially from those petroleum oils boiling in themotor fuel boiling range. In accordance with the present process,objectionable mercaptan compounds are removed from petroleum oilscontaining the same by treating these mercaptan-containing oils with aspent deleaded doctor solution. Preferred modifications of the presentinvention comprise desulfurization operations for the removal ofmercaptans utilizing a doctor solution in particular sequence andarrangement of stages.

It is known in the art to treat mercaptan-containing mineral oils,particularly mercaptan-containing petroleum oils boiling in the motorfuel boiling range by various procedures in order to remove themercaptan compounds or to convert them into less objectionabledisulfides. This is necessary since mercaptan constituents render theoil malodorous and undesirable. The usual method employed in thetreatment of petroleum oils for the removal of mercaptan compounds,

particularly for the-treatment of petroleum oils boiling in the motorfuel boiling range, is to contact the oil under suitable conditions witha socontent of the treated motor fuel and furthermore impairs thesusceptibility of the motor fuel toward knock-suppressing agents, as forexample, tetraethyl lead.

I have now discovered a process by which it is possible to employ arelatively small amount of doctor solution per volume of oil treated andto called, "doctor solution,. comprising an alkaline sodium plumbitesolution. This sodium plumbite solution is' generally prepared bydissolving lead oxide in an excess of sodium hydroxide. When thepetroleum oil and plumbite solution are mixed, a chemical reactionoccurs in which the mercaptans react with the sodium plumbite toform-oil-soluble lead mercaptides. These mercaptides are decomposedusually by the addition of free sulfur, resulting in the lead beingprecipitated as an insoluble lead sulfide and in the formation ofdisulfide compounds. This operation, known as sweetening may besummarized by the following reactions:

In this operation, in order to secure a high quality product it is verydesirable that the soluble lead compounds be entirely removed. This mayreadily be accomplished by proper control of reagents, time andtemperature but generally by the addition of a slight excess of freesulfur. However, the use of excess free sulfur even in relatively smallquantities is not desirable since it increases he corrosive orpolysulfide sulfur remove substantially completely the mercaptancompounds. My process secures a greater sulfur reduction per volume ofdoctor solution used than could heretofore be secured by using theconventional sweetening operation. In accordance with my process,mercaptan compounds are removed from feed oils containing the same byutilizing a spent doctor solution from which precipitated lead sulfide,preferably from which the entire amount of lead has been removed. Myinvention may be readily understood by reference to the drawingillustrating an embodiment of the same.

Referring specifically to the drawing the mercaptan-containing feed oilis introduced into initial treating zone 25 by means of line 26. Intreating zone 25 the oil is contacted with a spent doctor solution whichis introduced by means of line 21, which solution is substantially freeof lead and is secured' in a manner as hereinafter described. Themixture comprising the feed oil and the lead-free spent doctor solutionis withdrawn from treating zone 25 by means of line 28 and passed tosettling zone 29 wherein a separation is made between the spent doctorsolution and the oil. The spent doctor solution is withdrawn fromsettling zone 29 by means of line 30 and at least a portion of the samewithdrawn from the system by means of line 3| and disposed of in anymanner desirable. This is necessary to maintain the system in balance.The remainder of the spent doctor solution is introduced into zone 32wherein'it is treated for the removal of objectionable sulfur compoundswhich are removed overhead by means of line 33. This is preferablysecured by introducing steam by means of line 34. The treated spentdoctor solution is withdrawn from zone 32 by means of line 35 and passedto spent doctor storage 36 from where it' is recycled to treating zone25 along with additional lead-free spent doctor solution which isintroduced into zone 36 by means of line 31 and which is produced in amanner as hereinafter described. The treated oil separated in settlingzone 29 is removed by means of line 38 and introduced into secondarytreating zone 39 wherein it is contactedvwith doctor solution which isintroduced by means of line '40. Operating conditions are adjusted tosecure substantially complete conversion of the mercaptan compounds inthe oil. The treated oil is withdrawn from secondary treating zone 39 bymeans of line ii, mixed with sulfur which is introduced by means of line53, and then passed into settling zone 42 wherein a separation is madebetween the treated oil and the spent doctor solution. The treated oilsubstantially completely free of mercaptan compounds is withdrawn fromsettling zone 42 by means of line 43 and handled in any mannerdesirable.

The spent doctor solution is withdrawn from settling zone 42 by means ofline 44 and an appreciable proportion of the same passed intoregeneration zone 45 wherein the same is treated after adding leadsulfide from line preferably with an oxygen-containing gas which isintroduced by means of line 46 in order to regenerate the doctorsolution. The regenerated doctor solution is withdrawn from zone 45 bymeans of line ll and passed to doctor storage 48 from where it isrecycled to secondary treating zone 39 along with a fresh doctorsolution which is introduced by means of line 49.

A portion of thespent doctor solution removed from settling zone 42 bymeans of line 44 is passed through filtering zone 50 wherein theprecipitated lead sulfide is separated and removed by means of line 5|.The spent doctor solution free of precipitated lead sulfide is removedfrom filtering zone 50 by means of line 52 and passed into tertiarytreating zone 54 in which the doctor solution contacts a segregatedportion of the feed oil which is introduced by means of line 55 underconditions completely to free the spent doctor solution of lead. Themixture is withdrawn from tertiary treating zone 54 by means of line 56and introduced into settling zone 51 wherein a separation is madebetween the lead-free spent doctor solution and the oil. The oilcontaining dissolved therein soluble lead mercaptides is removed fromsettling zone 51 by means of line 58 and passed to-secondary treatingzone 39. The lead-free spent doctor solution is withdrawn from settlingzone 51 by means of line 37, passed to spent doctor storage 36, andpassed to initial treating zone 25 along with recycled spent doctorsolution as described above.

The process of the present invention may be widely varied. It is to beunderstood that the respective zones may comprise any suitable numherand arrangement of units. The character of the fresh doctor solutionemployed may be prepared in the conventionalmanner in which sufficientlead oxide is added to saturate a sodium hydroxide solution, preferablyof from about 12 to about 20 Baum. The quantity of fresh doctor solutionemployed per volume of oil may vary Widely and will depend upon thecharacter of the oil as well as upon other operating conditions. Asufficient amount should be used so as to completely convert theobjectionable mercaptan compounds to the innocuous disulfide compounds.A suflicient amount of the oil is used for contacting the lead sulfidefree spent doctor solution so that the doctor solution is substantiallycompletely freed of lead.

In doctor sweetening operations, in which the spent doctor solution isregenerated by oxidation, thiosulfates and other similar salts areproduced resulting in a corresponding reduction in the sodium hydroxidecontent. Therefore, in order to maintain the efiectiveness' of thedoctor solution, it' is necessary that the sodium, hydroxide content bekept above a certain minimum such as above about one pound of sodiumhydroxide per gallon and that the content of thiosulfates and othersalts be kept below a certain maximum, such as below about 1.5 pound pergallon. In order to stay within these limits, it is necessary to discardspent doctor solution and replace it with fresh doctor solution. Inaccordance with my invention, this spent doctor solution normallydiscarded is handled in a particular manner with respect to the feed oilbeing desulfurized, by which unexpected desirable results are secured.

It has been found that the spent doctor solution free of dissolved leadwhich is normally an objectionable waste product, can be satisfactorilyand eifectively used in accordance with my invention for the removal ofmercaptans from feed oils. The spent doctor solution has been found tobe several times as effective as an equal amount of fresh sodiumhydroxide solution of equal concentration. This is evident from theresults presented in the tables following:

Single stage extraction at 75 F. of a petroleum oil boiling in the heavynaphtha boiling range and containing 35 mg. of mercaptan sulfur per 100cc. oil utilizing 10% by volume of a sodium hydroxide solution and aspent doctor solution respectively Single stage extraction at 75 F. of apetroleum oil boiling in the heavy naphtha boiling range utilizing 20%by volume of a sodium hydroxide solution and a spent doctor solutionrespectively Pure N aOH Spent doctor solution solution Extractingsolution: N aOH content, #lgal 65 l. 15 1. 34v 65 l. 15 l. 34 Treatedpet. oil:

Mg. mercaptan S/lOO cc--- 22 20 19 20 3 1 Per centv mercaptan removed 3743 46 43 91 97 The results obtained by extracting the sour naphtha with10 or more percent of spent doctor solution containing 1.15 pound ormoreof NaQl-I per gallon in a single-stage operation are of particularinterest. These procedures removed% or more of the mercaptans present inthe naphtha. The use of two or more stages of countercurrent extractionin any of these cases re sults in the production of a sweet naphtha. Theextraction of this naphtha with pure sodium hydroxide of similarconcentrations and quantities resulted in the removal of only 31 to 46%of the mercaptans. In this case an extremely large quantity of puresodium hydroxide and a multi-stage countercurrent extraction system arerequired to obtain a sweet naphtha.

In extracting mercaptans with spent doctor solution, the eifectivenessof the. extraction decreases as the mercaptan content of the solutionincreases. However, the mercaptans can readily be recovered and thesolution regenerated to its original eifectiveness by steam distillationat atmospheric pressure or at elevated pressures.- 4

What I claim as new and wish to protect by Letters Patent is:

1. In a process for the removal of mercaptan compounds from a petroleumoil containing the same, the improvement which comprises removing leadfrom a spent doctor solution and contacting the oil with the resultingsolution whereby the mercaptan compounds are removed.

2. Process for the removal of mercaptan compounds from a petroleum feedoil, the improvement which comprises contacting the oil in an initialtreating zone with a spent doctor solution free of lead, separating thetreated oil and spent doctor solution in a settling zone, and recyclingat least a portion of the spent doctor solution to said initial treatingzone, contacting the treated oil removed from said initial treating zonein a secondary treating zone with a fresh doctor solution, separatingthe treated oil and the spent doctor solution and segregating a portionof the .spent doctor solution, removing the lead from the segregatedportion and recycling the deleaded spent doctor'solution to the initialtreating zone.

3. Process as defined by claim 2, in which said petroleum oil boils inthe motor fuel boiling range.

4. Process as defined by claim 2, in which the segregated portion of thespent doctor solution is freed of lead by filtering the lead sulfide andcontacting the filtered spent doctor solution with a segregated portionof fresh feed oil in a tertiary treating zone under conditions toconvert the lead plumbite into oil-soluble lead mercaptides, and underconditions in which the segregated portion of the feed oil containingsaid soluble lead mercaptides is passed to said secondary treating zone.

5. Process as defined by claim 2, in which the remaining portion of thespent doctor solution which has not been deleaded is passed to aregeneration zone wherein it is treated with an oxygen-containing gasunder conditions to regenerate the doctor solution, recycling saidregenerated doctor solution to said secondary treating zone.

HERBERT G. M. FISCHER.

